SiC-Si Grooved Surface Bonding
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SiC-Si Grooved Surface Bonding Tatiana S. Agrunova, Igor V. Grekhov, Lioudmila S. Kostina, Alexander G. Tur’yanskii1, Igor V. Pirshin1, Ilya R. Prudnikov2 and Konstantin B. Kostin3 Solid State Electronics Division, Ioffe Physico-Technical Institute RAS, Polytekhnicheskaya ul. 26, 194021, St. Petersburg, RUSSIA 1 Lebedev Physical Institute RAS, Leninskii pr. 53, 117924, Moscow, RUSSIA 2 Physics Department, Moscow State University, Vorob’evy Gory, 119899, Moscow, RUSSIA 3 Materials Science Department, Christian-Albrechts-University of Kiel, Kaiserstr. 2, Kiel 24143, GERMANY ABSTRACT SiC Lely platelets and SiC epilayers on large area SiC substrates were directly bonded to non-oxidized grooved surface silicon wafers in order to obtain structures prospective for the design of power bipolar devices with wide band-gap emitter junctions. The reported capabilities of grooved interfaces to reduce elastic strain and intrinsic sources of an interfacial potential barrier were utilized. The influence of surface morphology on the structural perfection of the bonded samples was studied in detail by X-ray and AFM techniques. As compared to traditional bonding technology, experimental data showed an easier smooth-to-grooved surface bonding accomplished in the formation of the boundary with better continuity and strength. For 2 in. diameter SiC wafers with root mean square height of roughness σ=16 Å and lateral coherence length L=1.8 µm bonding continuity not smaller than 90% was reached, while the crystals with σ=30 Å, L=5 µm failed to bond to Si even under an external force. INTRODUCTION Silicon carbide and compositions on its base due to their unique properties are being used for the design of high temperature circuits, power high voltage bipolar and field effect devices etc. A wafer bonding approach to fabricate SiC layers on large area insulating substrates was advanced in [1]. Si-SiO2- SiC compositions were made in such a way that β-SiC layers epitaxially grown on Si substrates were transferred onto oxidized Si wafers by bonding and etchback. Though successful as whole, the technology appeared to have shortcomings caused in particular by roughness of SiC surface. Bonding strengthening via multistep annealing between etches of Si substrate was proposed. An increasing flexibility of thinned SiC-Si portion of Si-SiO2-(SiC-Si) bonded structure was thus exploited to enhance the bonding energy. In this paper we demonstrate the other way by which the influence of the surface roughness can be appreciably reduced. The communication deals with structures prospective for the design of power bipolar devices with wide band-gap emitter junctions. 6H SiC wafers 0.3÷0.4 mm thick made of Lely grown crystals or composed by CVD layers on SiC substrates were directly bonded to silicon in order to provide oxide-free SiC-Si bonded compositions. It was earlier shown that, in the course of Si-Si bonding, an interfacial grooved relief eliminated elastic strain caused by surface morphology [2]. Besides, during annealing, the grooves acted as sinks for di
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